Do multiple Breakneck Mechs stack the "your mechs have deflect and ganking"?

Yes, multiple Breakneck Mech units stack their effects, but with some nuances regarding how the keywords themselves function.

Deflect

According to RiftJudge FAQ #8475 and Rule 735.2, Deflect stacks.

• Rule 735.2 states: "If a Unit has Deflect, or has been granted Deflect, and is granted Deflect by an additional source, the Deflect Value of all granted Deflect keywords is summed."
• Since Breakneck Mech grants "Deflect" (which defaults to a value of 1 per Rule 735.1.b.3), having two copies of Breakneck Mech on the board means your Mechs will have Deflect 2. An opponent must pay 2 additional Power to target them.

Ganking

While the Deflect stacks, the Ganking keyword does not stack in a meaningful way.

• Rule 736.2 explicitly states: "Multiple instances of Ganking are redundant."
• Because Ganking is a passive ability that simply adds a permission to a unit's Standard Move, having it granted by two different sources does not provide additional movement options or benefits beyond what a single instance provides.

Summary: If you have two Breakneck Mechs in play, your other Mechs will have Deflect 2 and Ganking (which functions the same as if they only had one instance of Ganking).